For the coffee sponge, whisk eggs and sugar, then add salt, flour and baking powder. Lightly butter a 20/24cm round springform tin pan, pour the mixture and bake at 190 C for about 30 minutes. Prepare the coffee cream. Whisk eggs and sugar, add coffee, milk and flour. Pour in a small sauce pan and keep whisking until it reaches a thick consistency, bearing in mind that when it cools, the cream thickens even more so be careful not to overcook it. Remove the sponge cake from the oven, slice it in 2 or 3, brush the layers with a mixture of milk and some liqueur, fill with the coffee cream previously cooled down completely and put the layers back together. Decorate with icing sugar.